Fossils of the Precambrian Ediacara Biota hold the key to understanding the origin and evolution of early animal life on this planet. Abundant fossils of these soft-bodied organisms occur globally and span 40 million years.
These fossils have traditionally been loosely grouped into three associations interpreted to have temporal significance -- with certain fossils representing older rocks and others representative of younger times.
Research reported here demonstrates that actually these extinct organisms had very strong environmental preferences and that these associations do not reflect time or the relative age of these fossils but rather the environmental preference. Fossils from all three assemblages occur in rocks representing four different environments in a single geographic area west of the Flinders Ranges in South Australia. Only two fossils occur in all four environments; the majority of the taxa occur in only one or sometimes two environments.
Thus, surprisingly, Earth's earliest marine ecosystem was very well differentiated into distinct communities, much as communities are today.
Furthermore, the absence of a particular type of organism may not indicate that it has gone extinct but rather may indicate that the preferred environment was not preserved.
Article: James G. Gehling and Mary L. Droser, DOI: 10.1130/G33881.1.